Interesting new $29 utility from Gravity Apps. Tags implements what is effectively a system-wide cross-application universal tagging system for Mac OS X. The UI is like Quicksilver or LaunchBar, in that you can invoke it from anywhere with a keyboard shortcut. But what’s novel is that you get to apply the same set of tags to everything from files in the Finder to Mail messages to Safari bookmarks. The tagging data is stored as file system metadata, and is thus searchable via Spotlight.

It’s not clear to me whether they’re using Mac OS X’s xattr metadata system in a way that’s strictly according to Hoyle, though — Tags is writing its metadata into Apple’s Spotlight namespace, because that’s the only way to get it indexed by Spotlight. To my knowledge that’s not officially supported.